To fine tune a Honda Keihin carburetor, adjust the idle screw, air/gasoline adjustment screw and other parts as necessary. A professional mechanic can help if the car owner is unable to do the work himself, says Keihin Carbs.
To fine-tune a Honda Keihin carburetor:
- Adjust the idle screw
- Adjust the air/gasoline screw
- Adjust the 1/8 to 1/4 throttle slow jet and throttle valve cutaway
- Adjust the 1/4 to 3/4 jet needle
Adjust the idle screw up to the desired minimum RPM depending on the type of ride. Make sure the engine is up to operating temperature.
Locate the air/gasoline screw, which may be upstream or downstream of the throttle valve. If upstream, turn counter-clockwise to lean the mixture off idle. If downstream, opening the screw will result in a richer fuel mixture.
If the idle screw has been adjusted but the engine still does not have a good response when the throttle is wide open, try replacing the slow jet with a larger one and adjusting the air/gasoline screw. If this doesn't work, try replacing the slide with a different number cutaway. A smaller cutaway will let less air in and create a richer fuel mix.
Replace the needle with a smaller model for a richer mixture. Adjust the clip position to change where the needle begins to taper.